Microhematocrit tubes are very small diameter tubes that draw blood thereinto by capillary action. They are used to draw blood from newborn infants or other individuals whose medical condition is such that the amount of blood given by them for test purposes must be held to a minimum.
To draw a minimal amount of blood from such a patient, a small prick is made to break the skin and permit a nominal amount of bleeding. The tube is held to the location of the prick and a small amount of blood is drawn thereinto by the phenomenon of capillary action.
The tube is taken to the lab and placed into a centrifuge; red blood cells or clotted blood cells are drawn to the bottom of the tube and clear plasma or serum, having a lower specific gravity than the cells, fills the balance of the tube. In many tests, the red blood cells or clotted blood cells are not needed and they are discarded. In these tests, only the clear plasma or serum is retained.
Most lab technicians score the tube with a file at the point where it is to be broken and then they manually break the tube; some dispense with the scoring and simply break the tube without first weakening it. Both of these methods are unsatisfactory because small droplets of blood and small shards of glass are produced by such breaking. The droplets of blood may be so small that they are suspended in air and may be aspirated by the medical personnel working in the room. Since blood may carry fatal diseases, a need exists for a better method of breaking microhematocrit tubes.